I remember some years ago, well about 1990-1991 to be precise, a husband and wife team used to come into our casino as card counters. They basically only survived because the casino where I worked at that time basically didnt know anything about advanced blackjack.
Although looking back, neither did this couple because they committed the cardinal of all sins, they failed to disguise their spread. I knew that these people were counting but I always thought that it was him that was the counter and she merely came with him for cover. As it turned out, it was his wife who was the counter and she merely signalled him when to bet. They started betting £5 and sooner or later they upped it to as far as the table maximum.
I dont know if this signal was audible or visual, she was sat so close to him that she could have easily touched his leg when it was time to bet. In the end though they got themselves barred which was hardly surprising looking back. Funnily enough I became friends with this player many years later and no doubt I would have had him in my first team had I known him personally at that time.
But it is bet spread that warns casinos of counters, actually their cover was pretty good. No casino suspects a husband and wife of being card counters and had they got their spread in order then they could have pulled this off for far longer than they did. They eventually split up and divorced which was sad but looking back, they never stood a chance. In fact they were lucky that I didnt blow the gaff but I didnt want the casino to know about what I knew about the game.
Back then we are talking pre-internet so the knowledge to beat the game and play professionally was little known and I had access to books from the States that few people in the UK had got or even read. This placed me into a very rare situation where I knew more than the casino management and that was a pretty good feeling for a croupier I can tell you 
take care and see you soon
Carl
